Within the cellulose production industry, the spent liquors from paper wood boiling (sulfate spent liquor and, in some cases, sulfite spent liquor) are combusted in a recovery boiler. The nature of the fuel and the process conditions result in a tendency of plugging of the air ports, which are openings through which combustion air is supplied. This clogging occurs through an accumulation of dust particles and flowing cinder products within the boiler. These pluggings are more accentuated in the lower regions of the air port and especially at the bottom. There are numerous known arrangements of cleaning devices which reciprocate through the air port for cleaning which are activated periodically as needed. It is important from environmental and process control points of view to achieve as complete a combustion as possible of the spent liquor within the recovery boiler. The supplemental supply of air through the air ports is an important parameter to achieve this goal. In addition to cleaning the air port, it is desirable to provide a regulating device which allows modulation of the air flow rate through the air port to achieve desired boiler operating parameters.
There are numerous examples of so-called port rodder devices for cleaning air ports which include damper assemblies for regulating air flow. In many examples of the prior art, the air regulating device provides a sharp edge orifice of variable area through which the air flows. Such an orifice configuration produces highly turbulent air flow into the combustion device. Due to its turbulence, this air flow is not able to penetrate deeply into the boiler interior, and thus produces a stratification of the air flow and available oxygen within the boiler interior. An ideal device of this type would produce an air stream into the boiler which has a velocity which enables it to penetrate into the interior of the boiler to provide a more homogeneous supply of combustion oxygen within the boiler interior. Additional examples of prior art rodder devices incorporate damper assemblies which must be retracted to a fully opened position before a cleaning cycle for the air port may be achieved. Thus, in such systems, the precisely adjusted damper position set for providing desirable furnace operating parameters is upset during the cleaning cycle. This can produce undesirable transient operating conditions within the boiler.